The present invention generally relates to a storage system and a data storage method, and in particular can be suitably applied to a storage system that uses a flash memory as its memory device.
In recent years, hard disk drives are becoming mainstream as the memory device of storage systems. Accordingly, technical innovation concerning hard disk drives is consistently pursued, and the storage capacity per unit area of hard disks is increasing drastically. In addition, reliability is also improving as a result of managing a plurality of hard disk drives in RAID (Redundant Array of Independent/Inexpensive Disks) format. Nevertheless, the read response of hard disk drives is slow at several ms or longer, and this slow read response is the bottleneck in the performance of storage systems using hard disk drives.
In order to overcome this bottleneck, recently, a flash memory as a semiconductor memory capable of freely rewriting data and in which data is not lost even when the power is turned off is being widely used as the memory device. The read response of a flash memory is 30 to 40 times faster than the read response of hard disk drives. Pursuant to the diffusion of such flash memories, the cost per unit bit thereof is decreasing.
In the future, it is anticipated that storage systems mounting flash memories as the memory device will appear in the market. As a result of adopting this kind of configuration, the creation of a storage system with a fast access speed and with low power consumption can be conceived.
Japanese Patent Laid-Open Publication No. 2007-66129 proposes a storage system mounting both a flash memory and a hard disk drive.